1. Field of the Invention
The present invention relates to a medical guide wire in which a metallic wire element of a helical spring body is improved at its mechanical strength properties by bonding a core wire to the helical spring body by means of a welding member.
2. Description of Related Art
In general, a medical guide wire (referred to simply as a guide wire) is thinned so that the guide wire is inserted into a somatic vasculature. With the thinned wire in mind, it is necessary to impart mechanical requirements to the guide wire with safety measures secured for a human body. For this purpose, various types of contrivances have been introduced.
In Japanese Pre-grant Patent Publication No. 4-25024 (referred to as a first reference hereinafter), the first reference discloses a medical guide wire in which a helical spring body has a radiotransparent coil and a radiopaque coil each connected at a distal end portion of a core wire by screwing the radiotransparent coil into the radiopaque coil. The screwed portion is bonded to the core wire by means of a soldering procedure. This makes it possible to bond members of different material like the case of bonding the radiotransparent coil to the radiopaque coil, while at the same time, ameliorating a visual recognition of the radiopaque coil under the fluoroscopic procedure.
The first reference, however, remains silent about a welding structure which suggests or teaches a correlation between the soldering material and mechanical strength properties of the metallic wire element of the helical spring body.
In Japanese Laid-open Patent Application No. 2004-194768 (referred to as a second reference hereinafter), the second reference discloses a medical guide wire having a core wire which has a mechanical strength (torsional rigidity) of more than 2800 MPa in order to improve a torque transmissibility. The core wire is made of stainless steel containing a high proportion of a silicic component which is different from the stainless steel represented by SUS304, SUS316 or the equivalent.
In Japanese Laid-open Patent Application No. 2006-297152 (referred to as a third reference hereinafter), the third reference discloses a connection structure in which a guide wire has a first coiled wire made of a thickened wire and a second coiled wire made of a thinned wire. The first coiled wire and the second coiled wire are bonded by means of a brazing procedure or the equivalent in order to render a brazing portion to curve evenly between the first coiled wire and the second coiled wire at the time of bending a flexible shaft.
As the case with the first reference, the third reference, however, remains silent about a welding structure which suggests or teaches a correlation between the soldering material and mechanical strength properties of the metallic wire element of the helical spring body. Let alone, the third reference shows no concrete measure to improve the mechanical strength properties of the welded portion between the core wire and the helical spring body by utilizing the melting heat produced upon soldering the core wire to the helical spring body.
In the prior medical guide wires, no technological idea has been introduced that a metallic wire element of a helical spring body (stainless steel wire) is highly drawn by means of a tightly drawing procedure to produce a highly drawn metallic wire element, and a eutectic alloy is used as a welding member (soldering or brazing material) with the thermal influence against the mechanical strength properties taken into consideration so as to improve a tensile rupture strength of the metallic wire element.
No technological idea has been made to utilize a melting heat produced when forming a synthetic resin layer on an outer surface of the helical spring body when the melting heat is conveyed as heat conduction to the helical spring body to improve the tensile rupture strength of the metallic wire element.
Further, no technological idea has been introduced so far to repetitively implement procedure (accumulating procedures) to successively improve the tensile rupture strength by observing a tensile rupture strength property due to the thermal influence against the metallic wire element, so as to impart the metallic wire element with a high tensile rupture strength. Much less, there has been no technological conception strived to concentrically place an inner helical spring body within the helical spring body so as to improve the tensile rupture strength of their metallic wire elements by utilizing the melting heat of the welding member.
Therefore, the present invention has been made with the above situation in mind, it is a main object of the invention to provide a medical guide wire which uses an austenitic stainless steel wire highly drawn as a helical spring body to improve its tensile rupture strength by utilizing the thermal influence given to the metallic wire element when it is highly drawn at the wire-drawing procedure, and further utilizing the thermal influence given by the welding member to improve the tensile rupture strength of the helical spring body which is formed by the metallic wire element.
It is another object of the invention to provide a medical guide wire which is capable to improve the tensile rupture strength of the helical spring body to impart the helical spring body with a fatigue-resistant property so as to enable an operator to use the helical spring body safely.